Blow valves are heavily loaded structural parts, the components of which are under high pressures and are subjected to rapid changes of direction and thus sharp accelerations. Blow valves are used or employed in blow moulding machines, in particular in blow moulding machines for shaping pre-forms into containers including bottles. In the sector of the foodstuffs industry and also in further sectors of industry it is necessary for the containers to be handled and produced in a germ-free manner. The shaping is preferably carried out by the supply of a pressurized fluid into the inner space of the pre-form, which in a particularly preferred manner is situated in a blow mould and which is expanded as far as the constricted shape of the blow mould on account of the fluid which is under pressure. In order to prevent a complicated cleaning of the shaped containers, considerable demands are set upon the cleanness of the pressurized fluid.
A valve for use in a blow moulding machine is known from the European Patent Office publication No. EP 1 271 029 A1. The valve known from EP 1 271 029 A1 has a movable piston, on one end of which is provided a sealing device for sealing off an opening in a housing through which a gas used for the shaping of the pre-form is conveyed. During an opening and closing movement the piston moves relative to a wall part and with this wall part it forms a slot which is sealed off by a sealing ring. In this case the use of a sealing ring is a major drawback since as a result of the relative movement of the piston and the wall a constant loading of the sealing ring occurs, on account of which the latter drops sharply in its functionality, i.e. in its sealing effect. In addition, even at low speeds of the piston there is no absolute guarantee that no impurities will penetrate into the sterile area, since the piston slides beyond the seal from the non-cleaned or non-sterile rear space into the cleaned or sterile valve space or control space and thus contaminates the latter.